A Sub-Threshold Oscillator-Based High-Accuracy Temperature Sensor With Tolerance to Supply Fluctuation and Device Aging

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Abstract
Accurate, low-power, and compact temperature sensors are demanded in a wide range of biomedical, environmental, and industrial sensing applications. This article presents an accurate and precise CMOS temperature sensor based on a sub-threshold ring oscillator (RO) in 180 nm. The sensing core employs a five-stage super cut-off contention-free (SCCF) delay cell to closely mimic the temperature dependency of a single MOSFET, minimizing the errors in current-to-frequency conversion and achieving a ${-} 0.065~^{\circ }$ C/ ${+} 0.061~{^{\circ }}$ C inaccuracy after 2-point calibration and ${\pm } 0.26~{^{\circ }}$ C after 1-point calibration from ${-} 20~{^{\circ }}$ C to $100~{^{\circ }}$ C. Meanwhile, a self-biased 3-transistor (3T) header significantly reduces the supply line sensitivity to $0.02~{^{\circ }}$ C/V and achieves less than $0.2~{^{\circ }}$ C temperature drift after more than 180 h of accelerated aging. The aging-induced drift is reduced to $0.11~{^{\circ }}$ C with a calibration after 30 h of pre-aging. Additionally, this work introduces an adaptive uniform resolution counter to maintain a consistent and programmable resolution across the wide temperature range, despite the sub-threshold RO’s exponential dependency on temperature. The prototyping sensor in 180-nm CMOS consumes only 33 nW at $20~{^{\circ }}$ C and occupies 0.028- $\text {mm}^{2}$ area. Beyond standard circuit testing, the 1-pt calibrated sensor was validated in a multi-day in vivo animal body temperature tracking experiment and outperformed off-the-shelf solutions.
Funding Information
  • Defense Advanced Research Projects Agency (FA8650-21-2-7119)

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